1. Security on Grid Roberto Barbera Univ. of Catania and INFN
SEE-GRID tutorial, Istanbul,
Security on Grid Roberto Barbera Univ. of Catania and INFN

2. Overview Glossary Encryption Certificates Grid Security
Symmetric algorithms
Asymmetric algorithms: PKI
Certificates
Digital Signatures
X509 certificates
Grid Security
Basic concepts
Grid Security Infrastructure
Proxy certificates
Command line interfaces
SEE-GRID tutorial, Istanbul,

3. Overview Glossary Encryption Certificates Grid Security
Symmetric algorithms
Asymmetric algorithms: PKI
Certificates
Digital Signatures
X509 certificates
Grid Security
Basic concepts
Grid Security Infrastructure
Proxy certificates
Command line interfaces
SEE-GRID tutorial, Istanbul,

4. Glossary Principal Credentials Authentication Authorization
An entity: a user, a program, or a machine
Credentials
Some data providing a proof of identity
Authentication
Verify the identity of the principal
Authorization
Map an entity to some set of privileges
Confidentiality
Encrypt the message so that only the recipient can understand it
Integrity
Ensure that the message has not been altered in the transmission
Non-repudiation
Impossibility of denying the authenticity of a digital signature
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5. Overview Glossary Encryption Certificates Grid Security
Symmetric algorithms
Asymmetric algorithms: PKI
Certificates
Digital Signatures
X509 certificates
Grid Security
Basic concepts
Grid Security Infrastructure
Proxy certificates
Command line interfaces
SEE-GRID tutorial, Istanbul,

6. Cryptography K1 Encryption DecryptionM C M
Mathematical algorithm that provides important building blocks for the implementation of a security infrastructure
Symbology
Plaintext: M
Cyphertext: C
Encryption with key K1 : E K1(M) = C
Decryption with key K2 : D K2(C) = M
Algorithms
Symmetric: K1 = K2
Asymmetric: K1 ≠ K2
Symmetric Algorithms
If the algorithm operates on the plaintex one bit (or byte) at a time it is called stream cipher, if it operates on blocks of bits, it is called block cipher.
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7. Public Key Infrastructure
Provides authentication, integrity, confidentiality, non-repudiation
Asymmetric encryption
Digital signatures
A hash derived from the message and encrypted with the signer’s private key
Signature checked decrypting with the signer’s public key
Allows key exchange in an insecure medium using a trust mode
Keys trusted only if signed by a trusted third party (Certification Authority)
A CA certifies that a key belongs to a given principal
Certificate
Public key + principal information + CA signature
X.509 format most used
PKI used by SSL, PGP, WS security, S/MIME, etc.
Encrypted text
Private Key
Public Key
Clear text message
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8. Symmetric Algoritms The same key is used for encryption and decryption
Advantages:
Fast
Disadvantages:
how to distribute the keys?
the number of keys is O(n2)
Examples:
DES
3DES
Rijndael (AES)
Blowfish
Kerberos A B
ciao
3$r
The lengths of the key vary from 56 bits (DES), now obsolete, to 256 bits.
As computing power increases, the lengths of the key must be increased too, to avoid brute force attacks (i.e. trying all the possible keys until the right one is found).
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9. Public Key Algorithms
Every user has two keys: one private and one public:
it is impossible to derive the private key from the public one;
a message encrypted by one key can be decripted only by the other one.
No exchange of secrets is necessary
the sender cyphers using the public key of the receiver;
the receiver decripts using his private key;
the number of keys is O(n).
Examples:
Diffie-Helmann (1977)
RSA (1978) A B
ciao
3$r
cy7
The lengths of the keys, at the moment, varies from 512 bits (insecure) to 2048 bits.
As the keys are much longer respect to those for symmetric algorithms, this kind of algorithms are much slower. For practical pourposes they are used togheter: first a temporary key for a symmetric algorithm is generated, which is used to encrypt the message, then the public key of the receiver is used to encrypt this key, which is sent (in encrypted form) together with the message.
A’s keys
B’s keys
public
public
private
private
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10. Overview Glossary Encryption Certificates Grid Security
Symmetric algorithms
Asymmetric algorithms: PKI
Certificates
Digital Signatures
X509 certificates
Grid Security
Basic concepts
Grid Security Infrastructure
Proxy certificates
Command line interfaces
SEE-GRID tutorial, Istanbul,

11. One-Way Hash Functions
Functions (H) that given as input a variable-length message (M) produce as output a string of fixed length (h)
the length of h must be at least 128 bits (to avoid birthday attacks)
given M, it must be easy to calculate H(M) = h
given h, it must be difficult to calculate M = H-1(h)
given M, it must be difficult to find M’ such that H(M) = H(M’)
Examples:
SNEFRU: hash of 128 or 256 bits;
MD4/MD5: hash of 128 bits;
SHA (Standard FIPS): hash of 160 bits.
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12. Digital Signature A calculates the hash of the message
A encrypts the hash using his private key: the encrypted hash is the digital signature.
A sends the signed message to B.
B calculates the hash of the message and verifies it with the one received by A and decyphered with A’s public key.
If the two hashes are equal, the message wasn’t modified and A cannot repudiate it. A
This is some
message
Digital Signature
This is some
message
Hash(A)
Digital Signature B
This is some
message
Digital Signature
A’s keys
public
private
Hash(B)
= ?
Hash(A)
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13. Digital Certificates A’s digital signature is safe if:
A’s private key is not compromised
B knows A’s public key
How can B be sure that A’s public key is really A’s public key and not someone else’s?
A third party guarantees the correspondence between public key and owner’s identity, by signing a document which contains the owner’s identity and his public key (Digital Certificate)
Both A and B must trust this third party
Two models:
X.509: hierarchical organization;
PGP: “web of trust”.
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14. PGP “web of trust” D B F C E A
F knows D and E, who knows A and C, who knows A and B.
F is reasonably sure that the key from A is really from A.
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15. The “third party” is called Certification Authority (CA).
X.509
The “third party” is called Certification Authority (CA).
Issue certificates for users, programs and machines
Check the identity and the personal data of the requestor
Registration Authorities (RAs) do the actual validation
CA’s periodically publish a list of compromised certificates
Certificate Revocation Lists (CRL)
They contain all the revoked certificates yet to expire
Online Certificate Status Protocol (OCSP).
CA certificates are self-signed
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16. X.509 Certificates An X.509 Certificate contains: owner’s public key;
identity of the owner;
info on the CA;
time of validity;
Serial number;
digital signature of the CA
Structure of a X.509 certificate
Public key
Subject:C=CH, O=CERN, OU=GRID, CN=Andrea Sciaba 8968
Issuer: C=CH, O=CERN, OU=GRID, CN=CERN CA
Expiration date: Aug 26 08:08: GMT
Serial number: 625 (0x271)
Sample user certificate
Certificate: Version: 3 (0x2) Serial Number: 981 (0x3d5) Signature Algorithm: md5WithRSAEncryption Issuer: C=IT, O=INFN, CN=INFN Certification Authority Issuer (CA) Validity Not Before: Oct 10 15:50: GMT Not After : Oct 10 15:50: GMT Subject: C=IT,O=INFN,CN=M User’s name Subject Public Key Info: Public Key Algorithm: rsaEncryption RSA Public Key: (1024 bit) User’s public key Modulus (1024 bit): :bf:7e:b9:91:9f:dd:07:10:aa:0f:e6:5b:dc:b6: [...] Exponent: (0x10001) X509v3 extensions: X509v3 Basic Constraints: critical CA:FALSE X509v3 Key Usage: critical Certificate use Digital Signature, Non Repudiation, Key Encipherment, Data Encipherment X509v3 CRL Distribution Points: CRL information URI: X509v3 Certificate Policies: Policy information Policy: X509v3 Subject Key Identifier: A:57:A5:DC:C2:76:44:E1:29:B9:C4:BC:13:58:70:2A:A0:01:37:B X509v3 Authority Key Identifier: keyid:CA:11:EF:5D:1D:07:04:98:A9:A5:B5:58:1A:66:4E:0A:16:2B:E0: DirName:/C=IT/O=INFN/CN=INFN Certification Authority serial: X509v3 Subject Alternative Name: X509v3 Issuer Alternative Name: URI: Signature Algorithm: md5WithRSAEncryption Signature of the CA :f7:ee:d2:57:f4:99:fc:1a:73:90:ab:ae:c4:8f:dc:de:b5: [...]
CA Digital signature
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17. Overview Glossary Encryption Certificates Grid Security
Symmetric algorithms
Asymmetric algorithms: PKI
Certificates
Digital Signatures
X509 certificates
Grid Security
Basic concepts
Grid Security Infrastructure
Proxy certificates
Command line interfaces
SEE-GRID tutorial, Istanbul,

18. GRID Security: the players
Large and dynamic population
Different accounts at different sites
Personal and confidential data
Heterogeneous privileges (roles)
Desire Single Sign-On
Users
“Group” data
Access Patterns
Membership
“Groups”
Grid
Sites
Heterogeneous Resources
Access Patterns
Local policies
Membership
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19. The Risks Launch attacks to other sites
Large distributed farms of machines
Illegal or inappropriate data distribution and access sensitive information
Massive distributed storage capacity
Disruption by exploiting security holes
Complex, heterogeneous and dynamic environment
Damage caused by viruses, worms etc.
Highly connected and novel infrastructure
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20. The Grid Security Infrastructure (GSI)B
Based on X.509 PKI:
A’s certificate
every user/host/service has an X.509 certificate;
certificates are signed by trusted (by the local sites) CA’s;
every Grid transaction is mutually authenticated:
A sends his certificate;
B verifies signature in A’s certificate;
B sends to A a challenge string;
A encrypts the challenge string with his private key;
A sends encrypted challenge to B
B uses A’s public key to decrypt the challenge.
B compares the decrypted string with the original challenge
If they match, B verified A’s identity and A can not repudiate it.
VERY IMPORTANT
Private keys must be stored only:
in protected places
AND
in encrypted form
Verify CA signature
Random phrase
Encrypt with A’ s private key
Encrypted phrase
Decrypt with A’ s public key
Compare with original phrase
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21. Certificate request … more details
Egee/LCG recognizes a given set of CAs
How do you request a certificate depends on your CA
The certificate request is created together with the certificate private key (encrypted by a pass phrase)
For GILDA, have a look at the Demo Video:
(Flash)
(Real)
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22. Certification Authority State of Illinois Certificate Request Cert
User generates public/private key pair.
CA confirms identity, signs certificate and sends back to user.
Cert Request
Public Key
Certification
Authority
Cert
State of Illinois ID
Private Key encrypted on local disk
User send public key to CA along with proof of identity.
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23. Certificate Information
To get cert information run grid-cert-info
grid-cert-info -subject
/C=CH/O=CERN/OU=GRID/CN=Simone Campana 7461
Options for printing cert information -all -startdate -subject -enddate -issuer -help
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24. X.509 Proxy Certificate GSI extension to X.509 Identity Certificates
signed by the normal end entity cert (or by another proxy).
Enables single sign-on
Support some important features
Delegation
Mutual authentication
Has a limited lifetime (minimized risk of “compromised credentials”)
It is created by the grid-proxy-init command:
% grid-proxy-init
Enter PEM pass phrase: ******
Options for grid-proxy-init:
-hours <lifetime of credential>
-bits <length of key>
-help
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25. grid-proxy-init
User enters pass phrase, which is used to decrypt private key.
Private key is used to sign a proxy certificate with its own, new public/private key pair.
User’s private key not exposed after proxy has been signed
User
certificate file
Private Key
(Encrypted)
Pass
Phrase
User Proxy
Proxy placed in /tmp, read-only by user
the private key of the Proxy is not encrypted:
stored in local file: must be readable only by the owner;
proxy lifetime is short (typically 12 h) to minimize security risks.
NOTE: No network traffic!
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26. Proxy again … grid-proxy-init ≡ “login to the Grid”
To “logout” you have to destroy your proxy:
grid-proxy-destroy
This does NOT destroy any proxies that were delegated from this proxy.
You cannot revoke a remote proxy
Usually create proxies with short lifetimes
To gather information about your proxy:
grid-proxy-info
Options for printing proxy information -subject -issuer -type -timeleft -strength -help
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27. Delegation and limited proxy
Delegation = remote creation of a (second level) proxy credential
New key pair generated remotely on server
Clients signs proxy cert and returns it
Allows remote process to authenticate on behalf of the user
Remote process “impersonates” the user
The client can elect to delegate a “limited proxy”
Each service decides whether it will allow authentication with a limited proxy
Job manager service requires a full proxy
GridFTP server allows either full or limited proxy to be used
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28. Long term proxy Proxy has limited lifetime (default is 12 h)
Bad idea to have longer proxy
However, a grid task might need to use a proxy for a much longer time
Grid jobs in HEP Data Challenges on LCG last up to 2 days
myproxy server:
Allows to create and store a long term proxy certificate:
myproxy-init -s <host_name> -d -n
-s: <host_name> specifies the hostname of the myproxy server
-d: server to use the subject of the certificate as the default username
-n: avoids the use of a passphrase to access to the long-term proxy
so the WMS can perform the renewals automatically.
myproxy-get-delegation -s <host_name>
Get a new proxy from the MyProxy server
myproxy-destroy
A dedicated service on the RB can renews automatically the proxy
contacts the myproxy server
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29. GSI environment variables
User certificate files:
Certificate: X509_USER_CERT (default: $HOME/.globus/usercert.pem)
Private key: X509_USER_KEY (default: $HOME/.globus/userkey.pem)
Proxy: X509_USER_PROXY (default: /tmp/x509up_u<id>)
Host certificate files:
Certificate: X509_USER_CERT (default: /etc/grid-security/hostcert.pem)
Private key: X509_USER_KEY (default: /etc/grid-security/hostkey.pem)
Trusted certification authority certificates:
X509_CERT_DIR (default: /etc/grid-security/certificates)
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30. Further Information Grid
LCG Security:
LCG Registration:
Globus Security:
Background
GGF Security:
GSS-API:
GSS-API:
SUNWdev/GSSAPIPG/toc.html
IETF PKIX charter:
PKCS:
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